For the city of San Diego to clear the way for a new library downtown, the obsolete Police Vehicle Maintenance Facility had to be relocated. Land was available adjacent to the San Diego Police Pistol Range, but accommodating the maintenance facility required relocating the K-9/SWAT facility and rehabilitating historic buildings at the range.
The redevelopment plan included a 2.4-acre maintenance facility, anchored by a two-story, 28,000-square-foot building housing administrative offices and vehicle maintenance. It also included a fuel station, oil lubrication site, vehicle wash bay, and 113 parking spaces. The 2-acre K-9/SWAT facility featured a 6500-square-foot building, 40,000-square-foot training field, 6000 square feet of kennel space, and 66 parking spaces.
The redevelopment significantly increased the impervious area. Because stormwater runoff from the new facilities discharges directly into Chollas Creek, the project needed to comply with a Section 404 permit, required by the U.S. Army Corps of Engineers. The creek was identified in 1998 as a “water quality limited waterbody” due to concerns about metals, toxicity, and coliform.
To satisfy permit requirements, the city would have to comply with state water quality requirements and obtain Section 401 certification from the San Diego Regional Water Quality Control Board. Obtaining certification required installation of an acceptable stormwater best management practice (BMP). Temecula, Calif.-based BDS Engineering Inc. was hired by the city to assist in achieving water quality certification and maximizing land use.
WEIGHING THE ALTERNATIVES
Bioretention was dismissed due to site soil conditions. Detention was another possibility. “There was not enough room, horizontally, on the site for a detention basin because they take up a lot of room,” said Tom Jones, P.E., principal at BDS.
While one small detention pond was built, Jones noted the site couldn't accommodate detention basins or bioswales large enough to hold the amount of stormwater that required treatment. To obtain 401 certification and comply with the 404 permit, Jones knew they had to achieve a high level of pollutant removal while using minimal space. However, Jones knew many proprietary BMPs, such as flow-through settling devices, do not meet certification requirements.
Jones was familiar with one approved BMP that was both compact and accepted by the Regional Water Quality Board. He decided to propose the StormFilter, from Portland, Ore.-based Stormwater Management Inc. The passive filtration system consists of an underground concrete structure housing rechargeable, media-filled filter cartridges that trap and adsorb particulates and pollutants.
BDS specified four StormFilters. Three are catch-basin models holding one, two, and three cartridges respectively. This configuration combines a catch basin, high-flow bypass device, and StormFilter into a single structure. The fourth StormFilter, in a manhole configuration, holds three cartridges. Each configuration fits easily within the site's space constraints.
The cartridges were filled with a blend of perlite and zeolite filter media. Perlite is a naturally occurring puffed volcanic ash that removes total suspended solids, oil, and grease. Zeolite is a naturally occurring mineral that removes soluble metals, ammonium, and some organics.
The vehicle maintenance facility opened July 14. Jones said the StormFilter had a higher capacity than other devices for removing pollutants from stormwater runoff, which meant they could comply with the 404 permit requirements. Performance will be assessed during the next routine maintenance check. Based on Stormwater Management's records and experience with StormFilter installations in southern California, filter cartridge replacement typically is suggested every two to three years, with additional maintenance recommended in years of excessive rainfall.